Estimation of the momentum coefficient of synthetic jet in flow separation control over an airfoil

Abstract

A simple estimation method of momentum coefficient of synthetic jet actuator has been proposed. Flow separation over an airfoil can be suppressed sufficiently with the estimated momentum coefficient. At a certain angle of attack (AOA), momentum deficit of boundary layer at front of separation point can be quantified based on Bernoulli's theorem. The function of synthetic jet actuator is deemed to be momentum addition and two stages of the addition corresponding to blowing and suction phases are considered respectively. The required momentum coefficient as well as the associated injection angle is determined preliminarily with the assumption of synthetic jet actuator at front of separation point. Since synthetic jet actuator is usually installed near the leading edge, a modification is introduced to consider the influence of excitation location. Using this method, flow separation over a NACA0015 airfoil is suppressed nearly completely with AOA = 15° and synthetic jet actuator at x/ c = 10%. Different angle of attacks corresponding to pre-stall angle, post-stall angle, and deep stall angle have been examined, respectively. Results indicate that the method is effective at pre-stall angle and post-stall angle. However, momentum coefficient will be underestimated when the separation point is upstream to the location of the airfoil's maximum thickness. At deep stall angle, the method is invalid. The estimation method is useful for practices of flow separation control with synthetic jet actuator.